1. Field of the Invention
This invention relates generally to an indicator power saving system and more particularly to such a system suitable for being used in a battery-operated desk-top electronic calculator.
2. Description of the Prior Art
Recently, desk-top electronic calculators have become popular and different kinds or models of such calculators have been designed and sold in the market.
Among such electronic calculators, small-sized units are especially popular and many efforts have been made to form a smaller electronic calculator.
A small-sized desk-top electronic calculator is usually designed to be operated not only by an AC line but also by a battery, and when such a small-sized and battery-operated desk-top electronic calculator is designed, one of the most important factors is how to decrease the power consumption of the calculator.
Considering the power consumption of a calculator, most power is consumed by an indicator driving circuit including an indicator.
Therefore, when a small-sized calculator is designed, it becomes one of the most important factors how to decrease the power consumption of the indicator driving circuit.
Based upon the above fact, different methods have been devised in the prior art to decrease the power consumption of the indicator and driving circuit, and one of the most popular methods known in the prior art is to provide an indication control circuit which turns off or stops the indicator driving circuit automatically after a predetermined time period, for example, after 30 seconds from the start of the indication.
However, such a method has inherent disadvantages as follows:
1. When the indicator driving circuit is turned off or stopped, it is difficult for an operator of the calculator to distinguish whether or not the calculator is in an operational condition, so that the operator is apt to misoperate the calculator.
2. The operator of the calculator is apt to forget to turn off the power switch of the calculator when he finishes calculations, because the indicator is designed to be extinguished automatically after the predetermined time period from the start of the indication even though circuits other than the indicator driving circuit are still in an operational condition and supplied with power from the battery.
In addition to the above, the prior art methods pay no attention to on the voltage across the battery. In other words, the indication control circuit provided therein is operated in the same way even when the voltage across the battery goes down, though it is desirable for such a calculator that the power consumption is decreased when the voltage across the battery goes down.